Electron beam convergence apparatus



Aug. 5, 1969 P. G. M CABE ELECTRON BEAM CONVERGENCE APPARATUS 5Sheets-Sheet 1 Filed Aug. 5 l963 INVENTOR. a ah/ 4-. 4/ 014;-

l IFWED FROM 50055 END Aug. 5, 1969 P. G. M CABE 3,459,989

E LECTRON BEAM CONVERGENCE APPARATUS Filed Aug. 5. 1965 5 Sheets-Sheet:5

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I I J INYENTOR. r-IF/HOT/HHD 0 1 g y/ (3 United States Patent 015cc3,459,989 ELECTRON BEAM CONVERGENCE APPARATUS Philip G. McCabe,Indianapolis, Ind., assignor to Radio Corporation of America, acorporation of Delaware Filed Aug. 5, 1963, Ser. No. 299,770 Int. Cl.H01j 29/50 US. Cl. 31513 19 Claims This invention relates to color imagedisplay systems and particularly to means for making a plurality ofelectron beams of a multiple beam display device converge at all scannedpoints on the target electrode of said device.

An illustrative example of such a multiple beam display device is acolor kinescope. Color kinescopes of the shadow type normally have threeelectron guns positioned in the neck of the kinescope and a targetelectrode including an apertured shadow mask located between theelectron guns and a luminescent screen of phosphor dots. The dots arearranged in groups of three in register with respective apertures of themask. Static magnetic means are provided for making the three electronbeams converge at the center of the scanned area of the targetelectrode. The three beams, after passing through the shadow mask,respectively strike three phosphor dots, each emitting light of adifferent color. All three beams are deflected by a common horizontaland vertical deflection system so that the beams systematically scan thekinescope target. The more the three beams are deflected from the centerof the target, unless corrective measures are taken, the greater may bethe misconvergence of the beams when they reach the shadow mask. It is,therefore, customary to provide dynamic electromagnetic means forcorrecting the misconvergence of the beams as a function of the angulardeflection of the beams from the center of the kinescope target. Forthis purpose, current waveforms of generally parabolic shape areproduced from energy derived from the horizontal and vertical deflectioncircuits and are employed, in conjunction with three convergenceelectromagnets, to dynamically converge the three beams at all points ofthe entire scanned area of the kinescope target.

The waveforms employed must have proper shapes and amplitudes in orderto achieve good convergence of the three beams at all points of thekinescope target. The waveform requirements may be estimated byobserving the unconverged rasters of the three beams. It has beenobserved that color picture tube systems operating with relatively largeangles of deflection, as for example 70 or more, require more correctionat the outer edges of the scanned area when the undeflected beams arestatically converged at the center of the picture area. Because of thisrequirement, the dynamic waveform must have greater amplitude andprecision in order to effect satisfactory convergence throughout thescanned picture area. Not only are the wave-shaping requirements moresevere in more recent systems having greater angles of beam deflection,but also considerably more deflecting force (i.e., Wave amplitude) isneeded to suitably eifect the desired beam convergence.

Recent trends in the design of color television receivers have been toemploy dynamic beam convergence circuits which include no activeelements. Such circuits perform essentially the function of providingsuitably shaped waves for application to the convergence electromagnets.The energy for these electromagnets consequently must come entirely fromthe horizontal and vertical deflection circuits. As the angle of beamdeflection increases, more 3,459,989 Patented Aug. 5, 1969 Therefore, itis an object of the invention to provide an improved high efliciencycircuit by which to effect convergence of a plurality of electron beamsof a color kinescope throughout a raster produced by relatively wideangle deflection of said beams.

The present invention reduces the energy demands placed upon thedeflection circuits by providing improved wave shaping accomplished bythe use of inactive circuit elements in the convergence circuits. Ateach of the horizontal and vertical deflection frequencies thesubstantially parabolic convergence current waves through theelectromagnet windings are produced by deriving substantially sawtoothvoltage waves from the respective deflection circuits. The improved waveshaping is achieved at the vertical deflection rate by clipping thesubstantially sawtooth voltage wave derived from the vertical deflectioncircuit during the first part of the deflection cycle and by suitablysloping the clipped portion of the wave. The vertical frequencyconvergence circuits include wave shaping networks including suchclipping facilities so as to provide more symmetrical convergenceparabolic current waves with steeper sides than heretofore has beenachieved in order to provide better beam convergence at the top andbottom portions of the picture area for a kinescope operating with (ormore) beam deflection.

More specifically, the improved wave shaping of the present invention isachieved by means including a series arrangement of a clipping deviceand a resistor connected effectively in parallel with the convergenceelectromagnet apparatus operating at the vertical deflection rate.

For a better understanding of the invention together with additionalobjects, features and advantages thereof, reference now will be made tothe following detailed description taken in connection with theaccompanying drawings, in which;

FIGURE 1 is a block diagram of a color television receiver in which thepresent invention may be embodied;

FIGURE 2 is a fragmentary sectional view of the neck portion of a colorkinescope, showing the relationship of the convergence electromagnetsand the electron beams controlled thereby;

FIGURE 3 is a schematic ciruit diagram of apparatus embodying theinvention for controlling the convergence electromagnets at the verticaldeflection frequency;

FIGURES 4 and 5 are fragmentary circuit diagrams of other embodiments ofthe invention; and

FIGURES 6 and 7 are sets of curves for reference in describing theoperation of the invention.

Reference first is made to FIGURE 1 for a general description of a colortelevision receiver embodying the present invention. Radiated signalsreceived by the antenna 11 are processed in the TV receiver circuits 12in a known manner to produce (1) video signals representing threecomponent colors of an image to be reproduced and (2) synchronizingsignals for controlling beam deflection and for other purposes such asthe production of suitable signals by which to eflect convergence of thethree electron 'beams at the target electrode of the imagereproducingcolor kinescope. The receiver circuits 12 may be of the type disclosedin Color Television Service Data, 1961, No. T6, furnished by RCA SalesCorporation, Indianapolis, Ind.

The color television receiver also includes a threebeam color kinescope13 serving as a color image-reproducing device such as a shadow maskcolor kinescope of the RCA type 2lFBP22 or 21FJP22 for example. The red,green and blue representative signals received from the receivercircuits 12 are impressed respectively upon electron guns 14, 15 and 16of the tricolor kinescope 13. The three electron beams produced by theseguns are deflected together over the target screen of the kinescopeunder the control of a deflection yoke 17. Also, the beams aremaintained in convergence with each other by means of a suitablyenergized beam convergence yoke 18, an illustrative form of which willbe described subsequently.

Also derived from the receiver circuits 12 are horizontal and verticalsynchronizing signals which are impressed upon a synchronizing signalseparator 19. The horizontal synchronizing signals are impressed uponthe horizontal deflection circuit 21 and the vertical synchronizingsignals are impressed upon the vertical deflection circuit 22. Thehorizontal and vertical deflection circuits are connected to thedeflection yoke 17 as indicated by the reference characters HM and V--V.All of the apparatus of FIG- URE 1 described up to this point may be ofthe same character as that disclosed in the service data previouslyreferred to.

Signals derived from the horizontal deflection circuit 21 at thehorizontal deflection rate are impressed upon horizontal convergencecircuits 23, the output of which is connected to the electromagnets ofthe convergence yoke 18. Signals at the vertical deflection rate derivedfrom the vertical deflection circuit 22 are impressed upon the verticalconvergence circuits 24 for the production of suitable waves which alsoare impressed upon the electromagnets of the convergence yoke 18.Details of such vertical convergence circuits by which suitableconvergence waves are produced will be described subsequently. Thehorizontal convergence circuits are not part of the present inventionand may be of a known type per se such as disclosed in Patent No.2,903,622, granted Sept. 8, 1959, to I. C. Schopp.

Reference now is made to FIGURE 2 for a description of the physicalrelationship of the convergence electromagnets and the electron beamscontrolled respectively thereby as presently embodied in commercialcolor television receivers such as that disclosed in the referenced RCAservice data.

This figure is a transverse sectional view of the neck portion of acolor kinescope as it appears when viewed from the luminescent screenend of the kinescope. The three electron beams 25 pass respectivelybetween pairs of pole pieces 26, 27 and 28 located internally of theneck 29 of the kinescope 13. These pole pieces extend inwardly from theends of substantially U-shaped cores of green, red and blue convergenceelectromagnets 30, 31 and 32 respectively mounted externally around theneck of the kinescope. The convergence electromagnets are provided withhorizontal frequency energizing windings designated 33G, 33R and 33B andwith vertical frequency energizing windings designated 34G, 34R and 34Brespectively for the green, red and blue electromagnets 30, 31 and 32.Energization of the electromagnet windings produces a magnetic fieldbetween the corresponding pole pieces which moves the correspondingelectron beam radially. There also may be included as part of theconvergence electromagnet structure some means for effecting a staticconvergence of the electron beams 25. The static convergence means maybe permanent magnets associated with the respective convergenceelectromagnets or may comprise windings on the respective electromagnetsfor energization by direct current of the proper amplitude and polarityto effect the desired static convergence of the electron beams. Suchstatic convergence means is known and, since a description of it is notneeded for an understanding of this invention, it is not shown.

Reference now is made to FIGURE 3 of the drawings. There is shown avertical deflection output tube 35 having in its anode circuit a primarywinding 36 of an output transformer 37. One of the secondary windings 38of this transformer is coupled as indicated in the usual manner to thevertical windings of a deflection yoke (not shown) for deflecting thethree electron beams of the color kinescope to scan the luminescentscreen of the kinesope vertically at the rate of approximately 60 fieldsper second. It is to be understood that horizontal windings of the yokealso will be energized to deflect the beams to scan the screenhorizontally at the rate of approximately 15,750 lines per second in theusual manner. The cathode circuit of the vertical output tube includes aresistor 39 which is bypassed by a capacitor 40, connected betweenterminal 41 and ground and across which cathode circuit there isdeveloped a substantially sawtooth voltage wave 42 at the verticaldeflection frequency.

The cathode of the vertical output tube 35 is coupled by means of aseries resistor 43 which is shunted by a capacitor 44 to the verticalfrequency windings 34G, 34R and 34B, respectively, of the green, red andblue convergence electromagnets 30, 31 and 32, respectively. By means ofthe resistor 43 and shunting capacitor 44, the AC and DC components ofthe saw tooth voltage wave 42 are proportioned in a predetermined ratio.The proportioning is such that the currents which are caused to flowthrough the vertical frequency windings of the convergenceelectromagnets always have substantially the same magnitudes at the timethat the electron beams are tracing the horizontal lines of the rasterat the center of the screen, irrespective of the particular shapes ofthe convergence currents and their peak-to-peak amplitudes.

The impression of the sawtooth voltage wave 42 upon the convergenceapparatus causes an integration of this wave such that the green and redconvergence electromagnet windings 34G and 34R are traversed by asubstantially parabolic convergence current wave 45. The amplitude ofthe parabolic current wave for the green and red convergenceelectromagnet windings 346 and 34R respectively is controlled by amaster amplitude control potentiometer 46, the movable contact of whichis connected to terminal 47 to which also are connected the green andred electromagnet windings.

The vertical windings 34G and 34R of the green and red convergenceelectromagnets 30 and 31 respectively are connected in series to themovable contact of a master tilt control potentiometer 48, the resistiveelement of which is connected across the terminals of another secondarywinding 49 of the vertical deflection output transformer 37. The centerof this winding is grounded to provide a return path for the currentsflowing in the windings of the convergence electromagnets. Pulse voltagewaves 50 and 51 of opposite polarity are developed respectively in thecoils 49a and 49b of the transformer winding and are available at theterminals of the winding.

' The impression of such pulses upon the convergence apparatus causes anintegration of the pulses such that the convergence windings 34G and 34Rare traversed by a substantially sawtooth current wave 52, the amplitudeand polarity of which are determined by the adjustment of the mastertilt control potentiometer 48. The sawtooth current wave 52 is added tothe generally parabolic current wave in the usual manner to tilt orphase the parabolic wave to effect substantial beam convergence at mostpoints of the scanned raster, except at those points in areas adjacentto the outer edges of the rastor for which the beams are subjected torelatively wide angle deflection.

A differential amplitude control potentiometer 53 has its resistiveelement connected across the series arrangement of the windings 346 and34R of the green and red convergence electromagnets 30 and 31,respectively. The junction point 54 between the green and red windings34G and 34R is connected to the center point of still another secondarywinding 55 of the vertical deflection output transformer 37. Pulsevoltage waves a and 51a of opposite polarity are developed respectivelyin the coils a and 55b of this secondary winding and are available atthe terminals of the winding. The termnials of this secondary winding 55are connected to the terminals of the resistive component of adifferential tilt control potentiometer 56. The movable contacts of thetwo differential potentiometers 53 and 56 are conected together. Theadjustment of the movable contact of the differential amplitude controlpotentiometer 53 varies distribution of the parabolic current wave 45through the respective windings 34G and 34R of the green and redconvergence electromagnets 30 and 31. The adjustment of the movablecontact of the differential tilt control potentiometer 56 determines thedistribution between the windings 34G and 34R of the green and redconvergence electromagnets 30 and 31 of the sawtooth current wave 52 bycontrolling the combination with this Wave of another sawtooth currentwave resulting from the integration of voltage pulses 50a, 51a by theconvergence apparatus.

The vertical frequency winding 34B of the blue convergence electromagnet32 is energized by a substantially parabolic current wave 45a, theamplitude of which is adjusted by a blue amplitude control potentiometer57 connected to terminal 58 in common with the winding 34B. Thisparabolic wave is tilted or phased by means of a suitable sawtoothcomponent 52a, the amplitude and polarity of which is determined by theadjustment of a blue shape control potentiometer 59, the resistiveelement of which is connected across the terminals of the deflectiontransformer secondary winding 49.

The green, red and blue convergence electromagnets 30, 31 and 32 alsoare provided with respective windings 33G, 33R and 33B as previouslydescribed and which are energized by suitably shaped waves at thehorizontal defiection frequency. These windings may be energized by anysuitable means such as that shown in Patent No. 2,903,622, granted Sept.8, 1959', to J. C. Schopp.

In order to improve the shape of the convergence current wave by whichthe green and red convergence electromagnets 30 and 31 are energizedwhen relatively large beam deflection angles are employed, there also isprovided a series arrangement of a unilaterally conducting device suchas a diode 61 and a variable biasing resistor 62 connected from themovable contact of the master amplitude control potentiometer 46 toground. This series arrangement is thus effectively connected inparallel with the series arrangement of the green and red electromagnetwindings 34G and 34R, respectively, the movable tap of potentiometer 48being substantially at ground. Note the grounded center tap of secondarywinding 49.

The improved wave shaping effected by the diode 61 and resistor 62 maybetter be seen by additional refererence to FIGURE 6. The substantiallysawtooth voltage wave 42 appearing at the terminal 41, and impressedacross the potentiometer 46, has its negative-going portion clipped bythe diode 61 so as to form a modified sawtooth wave 63 for impressionupon the electromagnet windings 34G and 34R at terminal 47. Thisclipping action occurs during the first portion of the vertical scanninginterval. The desired slope of the clipped portion 64 of the Wave 63 iscontrolled by variation of the resistor 62, thereby providing a suitablecontrol of the wave shaping facility to fit the particular convergenceneeds of the apparatus in which the facility is embodied. Thepositive-going portion 65 of the modified sawtooth voltage wave 63 isnot materially altered by the described wave shaping circuit from itsoriginal shape in the wave 42. As a result of the integration of thewave 63 by the convergence apparatus, the substantially paraboliccurrent wave 66 traversing the green and red electromagnet windings 34Gand 34R has a more symmetrical shape with steeper sides than it wouldhave without the wave shaping circuit of this invention. Such waveshaping thus, enables the achievement of substantial convergence of thered and green electron beams with the blue electron beam in the top andbottom portions of the raster scanned by these beams.

FIGURE 4, to which reference now is made, illustrates another embodimentof a wave shaping circuit including the series arrangement of the diode61 and the variable resistor 62. In this case the circuit is connectedfrom the junction of resistor 43 and potentiometer 46 to ground so that,as in FINGURE 3, it is effectively in parallel with the seriesarrangement of the green and red electromagnet windings 34G and 34R. Thecircuit functions substantially in the same manner as that describedwith reference to FIGURE 6. It has been found that additionalimprovement may be made in the shape of the current waveform 66 by theconnection of a capacitor 67 of suitable value across the diode 61- Thisadditional improvement is the further steepening of the leading slope ofthe parabolic current wave 66, whereby better beam convergence isachieved in the top portion of the scanned raster. It should be notedwith reference to FIGURE 6 with the arrangement of either FIGURE 3 orFIGURE 4, the clipping action does not continue throughout the entirefirst half of the vertical scanning cycle, the halfway point of thecycle being indicated by the broken line 68 Still another embodiment ofthe invention is shown in FIGURE 5. In this case only the AC componentof the vertical deflection frequency sawtooth wave 42 appearing atterminal 41 is impressed upon the convergence circuitry connected toterminal 47. The AC component of this wave is impressed upon theconvergence apparatus by means of a capacitor 69. The wave shapingcircuit including the series arrangement of the diode 61 and theresistor 62 is connected in substantially the same manner as thatdescribed with reference to FIGURE 4.

The operation of the wave shaping apparatus shown in FIGURE 5 isillustrated by the curves of FIGURE 7 representing the voltage wave 71impressed upon the convergence electromagnet windings by which toproduce the substantially parabolic current wave 72 through thesewindings. As in the previously described embodiment of the invention,the diode 61 serve to clip the negative-going portion of thesubstantially sawtooth voltage wave 42 developed at terminal 41. Theclipped portion 73 of the voltage wave 71 extends to substantially themidpoint of the vertical deflection cycle indicated by the broken line68. This type of operation is achieved by virtue of the fact that thewave shaping circuit operates on only the AC component of the sawtoothwave 42, thereby permitting the clipping action to be effective atapproximately the AC axis of the wave rather than at a lower voltagepoint dependent upon a DC component.

As a result of the extension of the clipping action to substantially themid point of the vertical deflection cycle, a more symmetrical paraboliccurrent wave 72 is produced than can be obtained by the use of any ofthe circuit arrangements shown in FIGURES 3 and 4. As in otherembodiments of the invention, the variable resistor 62 enables thecontrol of the slope of the clipped portion 73 of the voltage wave 71.

What is claimed is:

1. In a dynamic convergence system for multigun color cathode ray tubes,which convergence system includes a plurality of beam convergenceelectromagnets having energizing coils and convergence wave generatingmeans for producing energizing current having a parabolic currentcomponent, with said energizing coils presenting both series .inductanceand series resistance to said energizing current, the combinationincluding means for providing a sawtooth wave having portions extendingabove and below a reference axis, means for coupling said sawtooth waveto one end of said coils, resistance means connected between said oneend of said coils and a reference potential, said resistance meanscoacting with the series inductance of said coils to integrate saidsawtooth wave, with a portion of said sawtooth wave remainingunintegrated depending on the ratio of resistance to inductance of saidcoils, and clipping circuit means adapted to exclude portions of saidsawtooth wave of a given polarity with respect to said reference axisfrom said coils, with said sawtooth wave thereby modified includingcomponents corresponding to the fundamental components of a parabolicwave, whereby additional parabolic components are added to theenergizing current of said coils.

2. In a vertical deflection system for a multibeam cathode ray tube, thebeam convergence system including in combination, resistor meanscarrying current of sawtooth waveform at the vertical deflectionfrequency; a coupling capacitor, a variable resistor, and a convergenceinductor connected in a series circuit across said resistor means forenergizing said inductor with current of the sawtooth waveform and atselected amplitude; and wave shaping means including a rectifier deviceand a further resistor connected to said circuit for conducting during asubstantial portion of said sawtooth waveform to clip sald sawtoothwaveform and establish a voltage reference axis therefor to approximatethe reference axis of a wave of parabolic shape.

3. In a vertical deflection system for a multibeam cathode ray tube, thebeam convergence system including in combination, resistor meanscarrying current of sawtooth waveform at the vertical deflectionfrequency; a coupling capacitor, a variable resistor, and a convergenceinductor connected to said resistor means for energizing said inductorwith current of selected amplitude and sawtooth waveform; and waveshaping means including a rectifier device connected in circuit withsaid convergence inductor, said rectifier device being conductive duringa substantial portion of said sawtooth waveform to clip said sawtoothwaveform and apply to said inductor a wave of parabola-like shape.

4. In a vertical deflection system for a television receiver, a dynamicconvergence circuit for a multibeam cathode ray tube including incombination, first resistor means across which appears a sawtoothwaveform of vertical deflection frequency, a capacitor and secondresistor means connected in series and the combination thereof coupledacross said first resistor means, said second resistor means having avariable tap, a convergence coil, means coupling said convergence coilbetween said variable tap and a fixed point of said second resistormeans, and a rectifier diode and third resistor means connected inseries and the combination thereof connected in shunt with at least aportion of said second resistor means, said diode being poled with thecathode thereof conductive through said capacitor for clipping a portionof the sawtooth waveform and applying the same to said convergence coil.

5. In a dynamic convergence system for multigun color cathode ray tubes,which convergence system includes a plurality of beam convergenceelectromagnets having energizing coils and convergence wave generatingmeans for producing energizing current having a parabolic currentcomponent, with said energizing coils presenting both series inductanceand series resistance to said energizing current, the combinationincluding means for providing a sawtooth wave having portions extendingabove and below a reference axis, means for coupling said sawtooth waveto one end of at least one of said coils, variable resistance meansconnected between said one end of said coil and a reference potential,the series inductance of said coil serving to integrate said sawtoothwave, with a portion of said sawtooth wave remaining unintegrateddepending on the ratio of resistance to inductance of said coil, andclipping circuit means adapted to exclude portions of said sawtooth waveof a given polarity with respect to said reference axis in said coil,with said sawtooth wave thereby modified including componentscorresponding to the fundamental components of a parabolic wave, wherebyadditional parabolic components are added to the energizing current forsaid coil.

6. A dynamic convergence system for a multibeam cathode ray tubeincluding in combination, a vertical deflection circuit providing asawtooth Waveform at the vertical deflection frequency of the electronbeams, an inductance winding to produce a magnetic field for convergingone beam with respect to another, circuit means coupled between saidvertical deflection circuit and said inductance winding to apply thesawtooth waveform to the latter so that said inductance winding tends tointegrate said sawtooth wave form for producing a field varying as afunction of a parabola, said inductance winding having internalresistance tending to cause incomplete integration of the sawtoothwaveform therein, said circuit means including a clipping networkcomprising impedance means and unidirectionally conductive means, saidclipping network clipping a substantial portion of said sawtoothwaveform of said vertical deflection circuit so that a clipped sawtoothwave form is applied to said inductance winding to render the fieldthereof more parabolic.

7. A dynamic convergence system for a multibeam cathode ray tubeincluding in combination, a vertical deflection circuit having a givensource impedance and providing a sawtooth waveform at the verticaldeflection frequency of the electron beams, an inductance winding toproduce a magnetic field for converging one beam with respect toanother, circuit means coupled between said vertical deflection circuitand said inductance Winding to apply the sawtooth waveform to the latterso that said inductance winding tends to integrate said sawtooth waveform for producing a filed varying as a function of a parabola, saidinductance winding having an internal resistance tending to causeincomplete integration of the sawtooth waveform therein, said circuitmeans including a clipping network comprising resistor means, capacitormeans and unidirectionally conductive means, said clipping network andthe source impedance of said deflection circuit having component valueschosen to clip a substantial portion of said sawtooth wave form of saidvertical deflection circuit so that a clipped sawtooth wave form isapplied to said inductance winding to render the field thereof moreparabolic.

8. In a television color image display system including a multiple beamcolor image reproducing device and deflection means for deflecting saidbeams in a series of vertically spaced horizontal lines duringsuccessive beam trace periods to form a raster,

the combination for converging said beams at all points of said rastercomprising;

a plurality of respective dynamic convergence electromagnets for saidbeams, each of said eletcromagnets having an energizing winding;

a source of a sawtooth wave;

means coupling said source to said windings; and

wave-shaping means including a series arrangement of a diode and aresistor connected to said coupling means in parallel with a circuitincluding a series arrangement of two of said windings to so modify saidsawtooth wave that its impression upon said two windings causes to flowthrough said two windings a current wave having a substantiallysymmertical parabolic form with relatively steep side portions occuringrespectively at the start and finish of each of said trace periods.

9. In a television color image display system including a multiple beamcolor image reproducing device and deflection means for deflecting saidbeams in a series of verr tically spaced horizontal lines duringsuccessive beam trace periods to form a raster,

the combination for converging said beams at all points of said rastercomprising; a dynamic convergence electromagnet having an energizingwinding; a source of a sawtooth wave; means coupling said source to saidwinding; and wave-shaping means including a parallel arrangement of adiode and a capacitor connected in series with a resistor, saidwave-shaping means being connected to said coupling means to so modifysaid sawtooth wave that its impression upon said winding causes to flowthrough siad winding a current wave having a substantially symmetricalparabolic form with relatively steep side portions occurringrespectively at the start and finish of each of said trace periods. 10.In a television color image display system including a multiple beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates during respective beam trace periods toform a raster,

the combination of converging said beams at all points of said rastercomprising;

a dynamic convergence electromagnet having an energizing winding;

a source of a sawtooth wave at one of said deflection rates, said wavehaving AC and DC components;

means coupling said source to said winding to impress a predeterminedratio of said AC and DC wave components upon said winding; and

wave-shaping means including a series arrangement of a diode and aresistor connected to said coupling means and to said winding to somodify the AC component of said sawtooth wave during the first part ofeach of one of said trace periods that the impression of said modifiedsawtooth Wave upon said winding causes to flow through said winding acurrent wave having a substantially symmetrical parabolic form withrelatively steep side portions occurring respectively at the start andfinish of each of said trace periods.

11. In a television color image display system including a multiple beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates during respective beam trace periods toform a raster,

the combination for converging said means at all points of said rastercomprising;

a plurality of respective dynamic convergence electromagnets for saidbeams, each of said electromagnets having an energizing winding;

a source of a sawtooth wave at one of said deflection rates, said wavehaving AC and DC components;

means coupling said source to said windings to impress a predeterminedratio of said AC and DC wave components upon said windings; and

wave-shaping means including a series arrangement of a diode and aresistor connected to said coupling means in parallel with a circuitincluding a series arrangement of two of said windings to so modify theAC component of said sawtooth wave during the first part of each of oneof said trace periods that its impression upon said two windings causesto flow through said two windings a current wave having a substantiallysymmetrical parabolic form with relatively steep side portions occurringrespectively at the start and finish of each of said trace periods.

12. In a television color image display system including a multiple beamcolor image reproducing device and deflection means or deflecting saidbeams at line and field rates during respective beam trace periods toform a raster,

the combination for converging said beams at 'all points of said rastercomprising;

a dynamic convergence electromagnet having an energizing winding;

a source of a sawtooth wave at said field deflection rate,

said wave having AC and DC components;

means coupling said source to said winding to impress only said AC wavecomponent upon said winding; and

wave-shaping means including a diode and a resistor connected to saidcoupling means to so modify the AC component of said sawtooth waveduring substantially the first half of each of said field trace periodsthat the impression of said modified sawtooth wave upon said windingcauses to flow through said Winding a current wave having asubstantially symmetrical parabolic form with relatively steep sideportions occurring respectively at the start and finish of each of saidtrace periods.

13. In a television color image display system including a multiple beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates to form a raster,

the combination for converging said beams at all points of said rastercomprising;

a dynamic convergence electromagnet having an energizing winding;

a source of a sawtooth wave having alternate trace and retrace periodsat said field deflection rate;

means coupling said source to said winding; and

clipping means connected to said coupling means to so modify saidsawtooth wave that its impression upon said winding causes to flowthrough said winding a current wave having a substantially symmetricalparabolic form with relatively steep side portions occurringrespectively at the start and finish of each of said trace periods.

14; Ina television color image display system including a multiple beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates to form a raster,

the combination for converging said beams at all points of said rastercomprising;

a dynamic convergence electromagnet having an energizing winding;

a source of a sawtooth Wave having alternate trace and retrace periodsat said field deflection rate;

means coupling said source to said winding; and

means for clipping said sawtooth wave during a portion of each of saidtrace periods so as to modify said sawtooth wave such that itsimpression upon said winding causes to flow through said winding acurrent Wave having a substantially symmetrical parabolic-form withrelatively steep side portions occurring respectively at the start andfinish of each of said trace periods.

15. In a television color image display system including a multiple beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates to form a raster,

circuit means for converging said beams at all points of said rastercomprising;

a dynamic convergence electromagnet having an energizing winding;

a source of a sawtooth wave having alternate trace and retrace periodsat said field deflection rate;

means coupling said source to said winding; and

Wave-shaping apparatus including diode means for clipping said sawtoothwave during a portion of each of said trace periods and resistor 'meansfor controlling the slope of the clipped portions of said sawtooth wave,said wave-shaping apparatus being so connected in said convergencecircuit means as to modify said sawtooth wave such that its impressionupon said winding causes to flow through said winding a current wavehaving a substantially symmetrical parabolic form with relatively steepside portions occurring respectively at the start and finish of each ofsaid trace periods.

16. In a television color image display system including a three beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates during respective beam trace periods toform a raster,

the combination for converging said beams at all points of said rastercomprising;

three respective dynamic convergence electromagnets for said beams, eachof said electromagnets having an energizing winding;

a source of a sawtooth wave at said field deflection rate, said wavehaving AC and DC components; means including an amplitude controllingpotentiometer coupling said source to two of said windings to impress apredetermined ratio of said AC and DC wave components upon said twowindings; and wave-shaping means including a series arrangement of adiode and a resistor connected in shunt with at least a portion of saidpotentiometer and to a series arrangement of said two windings to somodify the AC component of said sawtooth wave during the first part ofeach of said field rate trace periods that its impression upon said twowindings causes to flow through said two windings a current wave havinga substantially symmetrical parabolic form with relatively steep sideportions occurring respectively at the start and finish of each of saidfield rate trace periods.

17. In a television color image display system including a three beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates during respective beam trace periods toform a raster,

the combination for converging said beams at all points of said rastercomprising;

three respective dynamic convergence electromagnets for said beams, eachof said electromagnets having an energizing winding;

means connecting two of said windings in an energizing circuit; a sourceof a sawtooth wave at said field deflection rate, said wave having ACand DC components;

means including an amplitude controlling potentiometer coupling saidsource to two of said windings to impress a predetermined ratio of saidAC and DC wave components upon said two windings; and

wave-shaping means including a series arrangement of a diode and aresistor connected in shunt with only a portion of said potentiometerand in parallel with said energizing circuit to so modify the ACcomponent of said sawtooth wave during the first part of each of saidfield rate trace periods that its impression upon said two windingscauses to flow through said two windings a current Wave having asubstantially symmetrical parabolic form with relatively steep sideportions occurring respectively at the start and finish of each of saidfield rate trace periods.

18. In a television color image display system including a three beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates during respective beam trace periods toform a raster,

the combination for converging said beams at all points of said rastercomprising;

three respective dynamic convergence electromagnets for said beams, eachof said electromagnets having an energizing winding;

means connecting two of said windings in series in an energizingcircuit;

a source of a sawtooth wave at said field deflection rate,

said wave having AC and DC components;

means including an amplitude controlling potentiometer coupling saidsource to two of said windings to impress a predetermined ratio of saidAC and DC wave components upon said two windings; and

wave-shaping means including a series arrangement of a diode and aresistor connected in shunt with said potentiometer and in parallel withsaid energizing circuit to so modify the AC component of said sawtoothwave during the first part of each of said field rate trace periods thatits impression upon said two windings causes to flow through said twowindings a current wave having a substantially symmetrical parabolicform with relatively steep side portions occurring respectively at thestart and finish of each of said field rate trace periods.

19. In a television color image display system including a three beamcolor image reproducing device and deflection means for deflecting saidbeams at line and field rates during respective beam trace periods toform a raster,

the combination for converging said beams at all points of said rastercomprising;

three respective dynamic convergence electromagnets for said beams, eachof said electromagnets having an energizing winding;

means connecting two of said windings in series in an energizingcircuit; a source of a sawtooth wave at said field deflection rate, saidwave having AC and DC components;

means including an amplitude controlling potentiometer coupling saidsource to two of said windings to impress a predetermined ratio of saidAC and DC wave components upon said two windings; and

wave-shaping means including a series arrangement of a capacitivelybypassed diode and a resistor connected in shunt with said potentiometerand in parallel with said energizing circuit to so modify the ACcomponent of said sawtooth wave during the first part of each of saidfield rate trace periods that its impression upon said two windingscauses to flow through said two windings a current wave having asubstantially symmetrical parabolic form with relatively steep sideportions occurring respectively at the start and finish of each of saidfield rate trace periods.

No references cited.

RODNEY D. BENNETT, JR., Primary Examiner JOSEPH G. BAXTER, AssistantExaminer US. Cl. X.R. 315-27

1. IN DYNAMIC CONVERGENCE SYSTEM FOR MULTIGUN COLOR CATHODE RAY TUBES,WHICH CONVERGENCE ELECTROMAGNETS HAVING ENPLURALITY OF BEAM CONVERGENCEELECTROMAGNETS HAVING ENENERGIZING COILS AND CONVERGENCE WAVE GENERATINGMEANS FOR PRODUCING ENERGIZING CURRENT HAVING A PARABOLIC CURRENTCOMPONENT, WITH SAID ENERGIZING COILS PRESENTING BOTH SERIES INDUCTANCEAND SERIES RESISTANCE TO SAID ENERGIZING CURRENT, THE COMBINATIONINCLUDING MEANS FOR PROVIDING A SAWTOOTH WAVE HAVING PORTIONS EXTENDINGABOVE AND BELOW A REFERENCE AXIS, MEANS FOR COUPLING SAID SAWTOOTH WAVETO ONE END OF SAID COILS, RESISTANCE MEANS CONNECTED BETWEEN SAID ONE OFSAID COILS AND A REFERENCE POTENTIAL, SAID RESISTANCE MEANS COACTINGWITH THE SERIES IN-